This invention relates to intraocular lenses (IOLs) and to methods for producing IOLs. More particularly, the present invention relates to relatively straight forward and easy to practice methods for producing IOLs with optics comprising silicone polymeric materials and to such IOLs which have advantageous properties, for example, increased fixation member pull strengths, that is increased bond strengths between the optic of the IOL and the fixation member or members of the IOL.
The use of IOLs to improve vision and/or to replace damaged or diseased natural lenses in human eyes, particularly natural lenses impaired by cataracts, has achieved wide acceptance. Accordingly, a variety of IOLs has been developed for surgical implantation in the posterior or anterior chambers of the eye according to a patient's needs.
Known IOLs comprise an optical lens portion or optic which includes an optical zone, and one or more, preferably two, supporting structures, called fixation members or haptics, for contacting eye tissue to fix or hold the IOL in the proper position after implantation. The optic may comprise a soft, resilient material, such as a silicone polymeric material (in particular, an elastomeric silicone polymeric material) or a relatively hard or rigid material such as, for example, polymethylmethacrylate (PMMA). The haptics typically comprise a filament constructed of a resilient metal or polymeric substance, such as PMMA, polyimide or polypropylene.
Each of the filament haptics is preferably flexible to reduce trauma to sensitive eye structures and to be yielding during insertion of the IOL. In addition, filament haptics generally have a memory retaining capability, e.g., springiness, so that after implantation of an associated IOL, the filament haptics automatically tend to return to their normal orientation.
As an alternative to filament haptics, some IOLs are provided with footplate-type haptics. These footplates generally extend radially outwardly from the optic (in the plane of the optic) and terminate in rounded or blunted ends configured for placement in an eye chamber. The materials for such footplates have included soft materials, for example, 2-hydroxyethyl methacrylate or silicone. However, footplate-type haptics are attended by disadvantages, such as the addition of extra material weight to the IOL and reduced flexibility as compared to filament haptics leading to poor fixation and consequent migration or dislocation of the IOL.
Although the filament haptics are preferred over the footplate-type haptics for several reasons, certain difficulties remain. For example, filament haptics and soft or deformable optics tend to be formed from dissimilar materials which do not ordinarily chemically bond together. As a result, filament haptics have been designed having a variety of attachment end configurations or structures, e.g., anchor structures, for providing a physical or mechanical interlock between the haptic and optic. Polypropylene haptics, for example, have heretofore been secured into silicone polymer-based optics by means of a mechanical lock. This lock may comprise a small loop or other anchor formed at the attachment end or lens bonding region of the haptic, which is then placed in a mold. The precursor material of the silicone polymer-based optic is poured into the mold, through and/or around the lens bonding region of the included haptic or haptics, and is then cured. Christ et al U.S. Pat. No. 4,790,846 discloses the molding of an optic around a haptic having a small loop or other anchor to effect a secure haptic connection.
Christ et al U.S. Pat. No. 4,790,846 further discloses a method for making an IOL in which a region of an elongated filament haptic has a different configuration, e.g., a bulbous enlargement, which cooperates with the optic of the IOL to form a mechanical interlock between this different configuration and the optic. If desired, the bulbous enlargement may have its outer surface roughened to improve adhesion of the material of the optic.
Bruns et al U.S. Pat. No. 4,737,322 discloses an IOL including haptics with anchoring struts which are located in the optic and surround or partially surround the center of the optical zone portion of the optic. These struts provide sufficient anchoring of the haptic in the optic to withstand a tensile pull force of from 50 to 115 grams.
Blake et al U.S. Pat. No. 5,104,590 discloses improving the adhesive properties of polypropylene haptics to silicone lenses through surface treatment of the haptic with a combination of a high frequency corona discharge and a silicone primer. Christ et al U.S. Pat. No. 5,147,397 discloses exposing the lens bonding region of a haptic to a plasma at conditions effective to enhance the bondability of the lens bonding region to the optic. While these procedures can be effective in enhancing haptic/optic bond strength, they are relatively sophisticated and are relatively expensive to practice, thus adding to the complexity and cost of producing IOLs. In addition, substantial care must be exercised in controlling the corona discharge and plasma exposing procedures to avoid damaging the relatively fine filament haptics.
It would be advantageous to provide a relatively straight forward and easy to practice method of producing IOLs which effectively enhances the bond or pull strength between the fixation member or members and the optic.